Recent animal sensory literature has been analyzed to evaluate the plausibility of reports of unusual animal behavior prior to earthquakes. Some species of fish possess remarkable sensitivity to pressure waves with frequencies below 50 Hz, which would enable them to sense earthquakes at least 1 to 3 Richter Magnitudes smaller than those detectable by human beings. Fish also have organs which can detect slight movements of water, although the available experimental data do not allow us to determine quantitatively whether they are sensing accelerations of water or variations in water displacement. Thus observations of unusual behavior of fish before earthquakes may be explained if the fish are responding to small foreshocks.